Hi there, the operating system writes data to sectors in a random manner, so it's tough to say whether the sectors storing your notes are completely overwritten or not with new data. Put the facts aside at present, there are three options for you to perform the data recovery task.
Option 1: Recover the overwritten notes via iBoysoft Data Recovery Software
A professional data recovery utility is able to scan your hard drive on a full scale, and iBoysoft Data Recovery Software is such a stunning tool. You can give it a try to recover the overwritten notes on your machine.
Option 2: Recover the overwritten notes via the Time Machine backup drive
If you have enabled Time Machine to back up your device beforehand, recovering overwritten notes from the backup drive is workable.
Step 1: Connect your Mac with the Time Machine backup drive. Enter password if required.
Step 2: Open a window of the folder where your file was stored. (optional)
Step 3: Click the Time Machine icon at the menu bar > Enter Time Machine.
Step 4: Scroll over to find the specific file you need to recover from the Time machine or use the Up/Down arrows.
Step 5: Select the desired file and press Space Bar to preview it.
Step 6: Click Restore. You can check the file at its original location.
Option 3: Restore your Mac to a previous point
If you log into the same Apple ID on both Mac and iPhone, the notes will be synced in real-time, so the notes on Mac are erased without exception. However, if you activate the APFS Snapshot before, you can turn your device to an early point when the notes were't erased yet. See how to roll back your Mac to a previous point.